The present invention relates to the field of propellers in general, including both propulsion propellers and fans, in particular cooling fans, such as the type utilized in association with radiators for motor vehicles or also, in general, cooling fans utilized for example in electric transformers or electric equipment in general, or for example fans to ventilate civil or industrial plants.
In many of the aforesaid applications it is necessary to regulate the flow of air provided by the propeller or fan. In the case of the motor vehicle radiator, for example, regulation of the rotation speed of the fan according to variation in the temperature is already known, by providing an electric actuator, a temperature sensor and an electronic unit to control the actuator on the basis of the feed-back signal generated by the sensor. All known solutions are relatively complicated and also somewhat inefficient, as they require a relatively high expenditure of energy.
The object of the present invention is to produce a propeller or fan, in particular a cooling fan, that is able to provide a variable outflow of air with extremely simple, functional and efficient means.
With a view to attaining this object, the invention relates to a propeller or fan, in particular a cooling fan of the type indicated hereinbefore, comprising a hub, and a plurality of blades carried by the hub, characterized in that it comprises shape-memory actuator means to regulate the direction and/or shape of the blades. These actuator means may be arranged to act automatically according to variation in temperature, or can be piloted by causing heating of the shape-memory elements provided in them by circulation of an electric current through them.
The use of shape-memory actuators has been known in general for some time. The same Applicant has already proposed several patents in the field such as for the regulation of rear view mirrors of motor vehicles, shutter fins for air-conditioning devices of motor or other vehicles. Shape-memory metal alloys, typically nickel and titanium, have the property of being subjected to contraction when they reach a pre-established transition temperature between xe2x88x9220xc2x0 C. and +90xc2x0 C.
Thanks to the characteristics indicated hereinbefore, the application of the invention to a cooling fan regulated according to the temperature is extremely simple and efficient. In fact, when there is a variation in the temperature of the shape-memory actuator means associated with the fan, these means automatically vary the geometry of the fan to obtain the desired effect. In other words, the device according to the invention is in this case self-adapting, as the parameter that causes activation of the shape-memory material, namely the temperature, is the same parameter which requires the fan to be regulated when there is a variation in it.
In a first embodiment, each blade of the fan is connected to the hub by a shaft composed of a shape-memory material, deformable (for example by torsion) through the action of its heating, so that each blade rotates progressively from a condition in which it defines a propeller with a minimum pitch to a condition with maximum pitch as the temperature increases.
Regulation of the flow of air delivered by the fan is thus obtained in a very simple manner, by varying the pitch of the propeller defined by the fan, with a rotation of the blades determined automatically by a variation in temperature, so as to prevent complex regulation devices, such as those utilized in known technique to regulate the speed of the electric motor that operates the fan according to the temperature.
In an alternative embodiment, each blade is composed of a flexible material and incorporates a plurality of shape-memory wires, arranged along the blade, which cause progressive twisting of the blade as the temperature increases.
As the temperature decreases, return of the blade towards its position at rest can be accelerated by elastic return means associated with the blade. Nonetheless, this contrivance is not essential, as return of the blade towards its position at rest is in any case encouraged by the aerodynamic action on the blade.
As can be seen, the shape-memory actuators means arranged according to the invention do not require any electric power supply, which makes the device extremely efficient, as no energy consumption is required. Nonetheless, this does not exclude the possibility of applying the invention to a propeller or fan in which the shape-memory element is heated by feeding an electric current through the element.